Recently, existing energy resources such as petroleum or coal have been expected to be exhausted, and thus an interest in energy that can replace the existing energy resources has been increased. A fuel cell as one of this alternative energy particularly receives attention due to merits in that the fuel cell has high efficiency, a pollutant such as NOx and SOx is not discharged, and used fuel is plentiful.
The fuel cell is an apparatus electrochemically reacting fuel and an oxidizing agent to generate electric energy. In the fuel cell, hydrogen is used as fuel, oxygen is used as the oxidizing agent, and an electrode is formed of an anode performing a catalyst role in a hydrogen oxidation reaction (HOR) and a cathode performing a catalyst role in an oxygen reduction reaction (ORR). In the fuel cell, the electrode includes a catalyst performing the aforementioned catalyst role, and platinum is generally used as a catalyst material. However, since platinum has problems in that a cost is high and a limit to an impurity is low, a lot of research has been conducted to manufacture and use a catalyst providing electrochemical activity and stability that are superior to those of pure platinum while reducing a use amount of platinum. In the aforementioned research, a plan for increasing activity of itself of platinum or an electrode catalyst of an alloy type of platinum and a transition metal is mostly proposed, but recently, an interest in a nanoparticle structure type having electrochemical activity and stability, particularly a hollow nanoparticle, has been increased.
Examples of a method of synthesizing hollow metal nanoparticles include a method of reducing metal ions on a solution by a reducing agent, a method using a gamma ray, an electrochemical method, and the like, but in the existing methods, since it is difficult to synthesize nanoparticles having a uniform size and shape or an organic solvent is used, various reasons such as problems such as environmental pollution and high costs occur, and thus it is difficult to perform mass production of high quality nanoparticles economically.
Further, since the hollow metal nanoparticles become easily unstable by a heat treatment temperature or a reaction temperature, there are many cases where the hollow metal nanoparticles are dispersed in a carrier to be used. Therefore, there is a demand for development of a method of effectively carrying high quality hollow metal nanoparticles having a uniform size in a carrier.